Well for some "jamming" is the only way it can be done. Then with some, they just do what they want no matter what. Is your math that bad? Where did I say it would grow from a new hatchling(what idiot would think an aro to be born) to 24" in a year? Anybody who really wants to know the true growth rates of a silver aro have a look through the arowana sub-forum.
BTW I didn't say your tank was too small, I said it was a growout

which means it will eventually become too small once your aro is over 24".